Venous access ports for the infusion and/or withdrawal of fluids from a patient are well-known. These devices are typically used for drug infusion or small amounts of blood aspiration. Where large flows of fluid are required, larger ports can be used such as for hemodialysis or plasmapheresis.
Some ports may be implanted subcutaneously. Implantable venous access ports have the advantage that they can remain within the patient for prolonged periods of time, permitting multiple use and decreasing the risk for associated infection. These ports typically provide a septum defining an access site for multiple needle sticks without the need to continuously search for new access sites, since the septum is comprised of material such as silicone elastomer that self-seals each time as a needle is withdrawn. These ports also each include a stem, or discharge port, that extends through a distal wall and that has a passageway therethrough; the stem is secured to the proximal end of a catheter so that the discharge port passageway is in fluid communication with the catheter lumen. One such catheter infusion port is disclosed in U.S. Pat. No. 6,113,572.
Other types of ports are in use, known as dual ports or multi-ports. These provide two or more internal septa and chambers, all corresponding to different lumens of the attached catheter via respective separate discharge ports or alternatively, separate passageways in a single stem for communication with separate lumens of a dual or multi-lumen catheter, such as in U.S. Pat. No. 5,360,407.
Such venous access ports are commonly circular in shape, or at least the chamber, or each chamber, is commonly circular, and the chamber floor is planar. As a result of the circular shape of a chamber and a planar chamber floor, the liquid injected during infusion exhibits a vortex behavior, and it has become noticeable that some liquid remains in the chamber by virtue of being near the center of the circular chamber's planar floor while the flow vortex occurs about the periphery of the chamber floor.
It is desirable to minimize the amount of liquid remaining in the chamber of a venous access port during infusion.